The present disclosure relates generally to the field of waveguides that permit transmission or reception of electromagnetic radiation (particularly millimeter wavelength radiation) with certain characteristics in selective directions while not substantially impacting the transmission and reception of electromagnetic radiation with different characteristics. This disclosure further relates to the use of such waveguides in antenna applications.
Dielectric waveguide antennas are well-known in the art, as exemplified by U.S. Pat. No. 6,750,827; U.S. Pat. No. 6,211,836; U.S. Pat. No. 5,815,124; and U.S. Pat. No. 5,959,589, the disclosures of which are incorporated herein by reference. Such antennas operate by the evanescent coupling of electromagnetic waves out of an elongate (typically rod-like) dielectric waveguide to a rotating cylinder or drum, and then radiating the coupled electromagnetic energy in directions determined by surface features of the drum. By defining rows of features, wherein the features of each row have a different period, and by rotating the dram around an axis that is parallel to that of the waveguide, the radiation can be directed in a plane over an angular range determined by the different periods.
Scanning or beam-steering antennas, particularly dielectric waveguide antennas, are used to send and receive steerable millimeter wave electromagnetic beams in various types of communication applications, and in radar devices, such as collision avoidance radars. In such antennas, an antenna element includes an evanescent coupling portion having a selectively variable coupling geometry. A transmission line, such as a dielectric waveguide, is disposed closely adjacent to the coupling portion so as to permit evanescent coupling of an electromagnetic wave between the transmission line and the antenna elements, whereby electromagnetic radiation is transmitted or received by the antenna. The shape and direction of the transmitted or received beam are determined by the coupling geometry of the coupling portion. By controllably varying the coupling geometry, the shape and direction of the transmitted/received beam may be correspondingly varied.
It is well known to construct a dielectric waveguide to contain the propagation of an electromagnetic wave in a given direction. For example, a waveguide with a dielectric substrate or slab and a metal plate disposed adjacent the dielectric slab will prevent any leakage of the electromagnetic wave through the metal plate, while permitting the electromagnetic wave to travel, for example, along the plane of the dielectric slab. However, the metal plate will also prevent the passage of other electromagnetic waves through it, for example, an electromagnetic wave that may be incident on the metal plate at an angle.
When multiple, steerable or beam steering antennas are used in close proximity, the waveguide described above may obstruct the passage of other electromagnetic waves that are traveling in a direction that crosses the waveguide's metal plate. Therefore, there is a need for a waveguide that permits transmission or reception of electromagnetic radiation with certain characteristic in selective directions without substantially impacting the transmission and reception of electromagnetic radiation with different characteristics.